In recent years, pancreatic islet cell transplantation has become a viable option to eliminate the need for frequent insulin injections in type I diabetic patients. However, the shortage of organ donors limits widespread use of this therapy. There is hope that this limitation can be overcome by generating transplantable replacement insulin- producing beta-cells from human embryonic stem cells (hESCs). Studies of pancreas development in genetically engineered mice have provided the foundation for developing conditions that instruct hESCs to differentiate into pancreatic progenitors and beta-cells. While pancreatic progenitors can be efficiently generated in vitro, the efficiency of endocrine cell differentiation from these progenitors is still very low, thus compromising development of a cell-based therapy. Therefore, further developmental studies are crucial to identify the molecular cues that regulate the switch from a pancreatic progenitor to a committed endocrine cell. Here, I investigated the role of the transcription factor NRSF and a component in the NRSF corepressor complex, the histone demethylase LSD1, during pancreatic endocrine cell formation. Using in vitro and in vivo models of pancreas development, we show that NRSF is specifically repressed in endocrine cells and late progenitors committed to the endocrine fate. In pancreatic progenitors, NRSF occupies the regulatory regions of endocrine lineage-determining transcription factors. However, genetic ablation of NRSF revealed that NRSF is dispensable for pancreatic endocrine cell formation and function. In stark contrast, we show that the expression of LSD1, which has been shown to interact with a number of complexes, including the NRSF corepressor complex, is required for pancreatic endocrine cell formation. Genetic inactivation of Lsd1 in pancreatic progenitors leads to selective loss of the endocrine cell lineage, but only during a short competence window, which precedes endocrine cell differentiation by several days. Chromatin profiling of LSD1-deficient progenitors at the end of this competence window revealed a novel role for LSD1 in facilitating enhancer activation. These data suggest that transcription factors are not necessarily the only drivers of cell fate and that chromatin remodelers can also orchestrate cell fate decisions. Further, many factors have been thought to be master regulators of cell fate decisions, but LSD1 is the only factor to date that affects cell fate in multipotent progenitor cells prior to and independent of specification factors. Altogether, my findings not only uncover novel roles for these two genes during pancreatic endocrine cell formation, but also contribute to our basic understanding of how transcription factors and chromatin-modifying enzymes affect cell fate

BACKGROUND:With the advent of immune-checkpoint inhibitor (ICI) therapy (anti-CTLA-4, anti-PD-1), immune-related adverse events such as thyroid function test abnormalities (TFTAs) are common, with a reported incidence range of 2%-15% depending upon the ICI used. The aim of this study is to describe the incidence of TFTAs retrospectively in patients who received ICI therapy. METHODS:A total of 285 patients were reviewed (178 male, 107 female; 16-94 years of age), of whom 218 had no baseline TFTAs, 61 had baseline TFTAs, and 6 had a history of thyroidectomy (excluded). At least one dose of ipilimumab and/or nivolumab or pembrolizumab was administered. Post-ICI therapy TFTAs were classified according to standard definitions of thyroid conditions when possible. RESULTS:A total of 35% (76/218) patients had new-onset TFTAs on ICI therapy. Of note, 70.5% (43/61) had baseline TFTAs that were exacerbated by ICI therapy. The median times to new-onset or exacerbated baseline TFTA were 46 and 33 days, respectively. Of note, 64.5% (20/31) of patients on both ipilimumab and nivolumab had new-onset TFTAs, compared with 31.3% (15/48) on ipilimumab, 31.5% (28/89) on nivolumab, and 26% (13/50) on pembrolizumab. CONCLUSION:The incidence of TFTAs with ICI therapy was higher than previously reported. Patients with baseline TFTAs and/or who were receiving ipilimumab and nivolumab combination therapy had a higher incidence of TFTAs than patients receiving single-agent ICI therapy. We recommend more frequent evaluation of thyroid function in the first 8 weeks, especially in patients with baseline TFTAs. IMPLICATIONS FOR PRACTICE:Increased use of immune-checkpoint inhibitors in cancer treatment has highlighted the importance of monitoring for and treating immune-related adverse events. This study was conducted to assess the incidence of thyroid function test abnormalities retrospectively in patients with cancer on immune-checkpoint inhibitors, which is not known exactly. This study is unique in that it included patients with a variety of histologic subtypes of cancer and also followed the clinical course of patients with baseline thyroid function test abnormalities. This study can help make oncologists aware that the incidence of thyroid function test abnormalities is higher than anticipated. Early identification and timely treatment can help ameliorate symptoms for patients and improve their overall quality of life.

Embryonic development relies on the capacity of progenitor cells to appropriately respond to inductive cues, a cellular property known as developmental competence. Here, we report that epigenetic priming of enhancers signifies developmental competence during endodermal lineage diversification. Chromatin mapping during pancreatic and hepatic differentiation of human embryonic stem cells revealed the en masse acquisition of a poised chromatin state at enhancers specific to endoderm-derived cell lineages in gut tube intermediates. Experimentally, the acquisition of this poised enhancer state predicts the ability of endodermal intermediates to respond to inductive signals. Furthermore, these enhancers are first recognized by the pioneer transcription factors FOXA1 and FOXA2 when competence is acquired, while subsequent recruitment of lineage-inductive transcription factors, such as PDX1, leads to enhancer and target gene activation. Together, our results identify the acquisition of a poised chromatin state at enhancers as a mechanism by which progenitor cells acquire developmental competence.

Present-day Tibetans have adapted both genetically and culturally to the high altitude environment of the Tibetan Plateau, but fundamental questions about their origins remain unanswered. Recent archaeological and genetic research suggests the presence of an early population on the Plateau within the past 40 thousand years, followed by the arrival of subsequent groups within the past 10 thousand years. Here, we obtain new genome-wide data for 33 ancient individuals from high elevation sites on the southern fringe of the Tibetan Plateau in Nepal, who we show are most closely related to present-day Tibetans. They derive most of their ancestry from groups related to Late Neolithic populations at the northeastern edge of the Tibetan Plateau but also harbor a minor genetic component from a distinct and deep Paleolithic Eurasian ancestry. In contrast to their Tibetan neighbors, present-day non-Tibetan Tibeto-Burman speakers living at mid-elevations along the southern and eastern margins of the Plateau form a genetic cline that reflects a distinct genetic history. Finally, a comparison between ancient and present-day highlanders confirms ongoing positive selection of high altitude adaptive alleles.

Developmental progression depends on temporally defined changes in gene expression mediated by transient exposure of lineage intermediates to signals in the progenitor niche. To determine whether cell-intrinsic epigenetic mechanisms contribute to signal-induced transcriptional responses, here we manipulate the signalling environment and activity of the histone demethylase LSD1 during differentiation of hESC-gut tube intermediates into pancreatic endocrine cells. We identify a transient requirement for LSD1 in endocrine cell differentiation spanning a short time-window early in pancreas development, a phenotype we reproduced in mice. Examination of enhancer and transcriptome landscapes revealed that LSD1 silences transiently active retinoic acid (RA)-induced enhancers and their target genes. Furthermore, prolonged RA exposure phenocopies LSD1 inhibition, suggesting that LSD1 regulates endocrine cell differentiation by limiting the duration of RA signalling. Our findings identify LSD1-mediated enhancer silencing as a cell-intrinsic epigenetic feedback mechanism by which the duration of the transcriptional response to a developmental signal is limited.

Adaptation of the islet β cell insulin-secretory response to changing insulin demand is critical for blood glucose homeostasis, yet the mechanisms underlying this adaptation are unknown. Here, we have shown that nutrient-stimulated histone acetylation plays a key role in adapting insulin secretion through regulation of genes involved in β cell nutrient sensing and metabolism. Nutrient regulation of the epigenome occurred at sites occupied by the chromatin-modifying enzyme lysine-specific demethylase 1 (Lsd1) in islets. β Cell-specific deletion of Lsd1 led to insulin hypersecretion, aberrant expression of nutrient-response genes, and histone hyperacetylation. Islets from mice adapted to chronically increased insulin demand exhibited shared epigenetic and transcriptional changes. Moreover, we found that genetic variants associated with type 2 diabetes were enriched at LSD1-bound sites in human islets, suggesting that interpretation of nutrient signals is genetically determined and clinically relevant. Overall, these studies revealed that adaptive insulin secretion involves Lsd1-mediated coupling of nutrient state to regulation of the islet epigenome.